Growth of 2D heterostructures of graphene/BN

Metal free direct growth of graphene on h-BN using a high temperature (°1550°C) chemical vapor deposition technique was done under Ar environment. Growth temperature, methane partial pressure, hydrogen/methane flow ratio, and growth time were varied and optimized. Raman spectroscopy clearly showed the signature of graphene with G- (°1580cm^-1) and 2D-mode (°2700cm^-1). The smallest width of G- and 2D-peak was 30 and 55cm^-1, respectively, and the Raman I_2D/I_G ratio varied between 0.7 and 1.8. Raman D-peak (°1350cm^-1) shows a strong dependence on growth temperature with the smallest I_D/I _G value of 0.15 at 1550°C. In the case of long growth, nitrogen and boron doping were detected by x-ray photoelectron spectroscopy with a small Raman D'-peak. A continuous graphene film with the rms roughness (1×1 μm² area) of 0.32nm was shown by atomic force microscopy. Early stage of growth revealed circular shaped nucleation islands, the density and heights of which are °15/μm² and 1-2 graphene monolayer (ML), respectively. The hydrogen/methane flow ratio was found to be a critical parameter to obtain smooth 2D growth. Growth of h-BN is performed with ammonia borane, hydrogen and Ar. The growth is found to be critically dependent on the conditions of the ammonia boran precursor. Reproducible continuous films of h-BN are reported.